The present invention relates to a seat reclining apparatus for vehicles for freely adjusting an inclination angle of a seat back with respect to a seat cushion.
Conventionally, as this kind of seat reclining apparatus, for example, there has been known a structure shown in the Japanese Patent Laid-open Publication Nos. 1-104201 (1989) or 2-128707 (1990). These are structured such as to have a lower arm adapted to be held to a seat cushion frame, an upper arm rotatably supported to the lower arm and adapted to be held to a seat back frame, and a lock mechanism having pawls which are arranged between the lower arm and the upper arm and a ratchet engaged with the pawls so as to restrict a rotation of the upper arm with respect to the lower arm.
In the former conventional apparatus, a first recess or depressed portion in which an internal tooth portion constituting a ratchet is formed on an inner peripheral surface of the recess is formed in the upper arm in a partial pressing manner, and guide grooves slidably supporting the pawls are formed in the lower arm in a partial pressing manner. Further, a second recess or depressed portion having contact portions on the outer peripheral surface thereof is formed in the lower arm in a partial pressing manner, and the contact portions of the second recess and the inner peripheral surface of the first recess are slidably brought into contact with each other, thereby rotatably supporting the upper arm with respect to the lower arm. Still further, a supporting plate extending in such a manner as to cover the outer peripheral edge of the lower arm and holding the lower arm therebetween is fixed to the upper arm, and the supporting plate prevents the upper arm and the lower arm from coming off in an axial direction.
In the latter conventional apparatus, a ring-shaped first metal fitting having an inner peripheral surface on which an internal tooth portion constituting a ratchet and a bearing portion are formed is fixed to the upper arm, a second metal fitting in which a guide groove slidably supporting the pawl is formed and having an outer peripheral surface slidably brought into contact with the bearing portion of the first metal fitting is fixed to the lower arm, and the upper arm is rotatably supported to the lower arm by a slidable contact between the bearing portion of the first metal fitting and the outer peripheral surface of the second metal fitting. Further, the upper arm is held between the lower arm and the second metal fitting, thereby preventing the upper arm and the lower arm from coming off in an axial direction.
However, in the former conventional apparatus mentioned above, since the contact portion of the lower arm is slidably brought into contact with the inner peripheral edge of the recess so as to support the upper arm to the lower arm, it is necessary to make the lower arm larger than the upper arm, so that the total size of the apparatus is increased at that degree, and a cost and a weight are increased.
Further, in the latter conventional apparatus, since the first metal fitting and the second metal fitting are required, a number of the parts is increased, so that a cost and a weight are increased at that degree. Still further, since the upper arm is held between the second metal fitting and the lower arm, it is necessary to provide an opening having a large area in the upper arm, so that a strength of the upper arm is reduced at that degree.